Modern technologies are developing prosperously. Novel information products are introduced daily for satisfying people's various needs. Early displays are mainly cathode ray tubes (CRTs). Owing to their huge size, heavy power consumption, and radiation hazardous to the heath of long-term users, traditional CRTs are gradually replaced by liquid crystal displays (LCDs). LCDs have the advantages of small size, low radiation, and low power consumption, and thus becoming the mainstream in the market.
LCDs control the transmittance of liquid crystal cells according to data signals for displaying images. Because active-matrix LCD displays adopt active switching devices, such type of LCDs is advantageous for displaying motion pictures. Thin-film transistors (TFT) are the main switching devices used for active-matrix LCDs.
FIG. 1 shows a schematic diagram of the driving system for LCD according to the prior art. As shown in the figure, the driving system comprises a display panel 10, a scan driving circuit 12, a data driving circuit 14, a timing control circuit 16, and a gamma circuit 18. The display panel 10 is used for displaying images. The scan driving circuit 12 is used for producing and transmitting a plurality of scan signals to the display panel 10 for driving the display panel 10. The gamma circuit 18 is used for producing a plurality of gamma voltages. The data driving circuit 14 uses the plurality of gamma voltages produced by the gamma circuit 18 as the reference voltages and select the reference voltage according to a plurality of display dada for producing and transmitting a plurality of data signals to the display panel 10, so that the display panel 10 can display images according to the plurality of data signals. The timing control circuit 16 produces a timing control signal and transmits the scan control signal to the scan driving circuit 12 and the data control signal to the data driving circuit 14, respectively, for controlling the timing of the scan driving circuit 12 and the data driving circuit 14 transmitting the plurality of scan signals and the plurality of data signals, respectively, to the display panel 10.
FIG. 2 shows a waveform of the driving signal of the LCD according to the prior art. The gamma circuit 18 produces the reference voltages and supplies the reference voltages to a digital-to-analog converting circuit of the data driving circuit 14. The digital-to-analog converting circuit selects one of the reference voltages, produces a select voltage Vsel, and transmits the select voltage Vsel to a buffer of the data driving circuit 14. The buffer produces the driving signal according to the select voltage Vsel for driving the display panel 10. For the data driving circuit 14, the display panel 10 is equivalent to a first-order RC circuit.
As shown in FIG. 2, the basic charging process of the display panel 10 is shown. For brevity, the charging process, which includes the charge recycling process and the pre-drive process, is simplified. AVDD is the voltage produced by the power supply circuit for the buffer; Vsel is the select voltage selected by the digital-to-analog converting circuit and produced by selecting from the reference voltages; and SL is the voltage across the equivalent capacitor of the display panel 10. Assuming that the voltage across the equivalent capacitor is zero when the display panel 10 starts being charged, almost all of the voltage is across the equivalent resistor and the buffer. During the charging process of the display panel 10, the voltage across the equivalent capacitor is raised gradually, which makes the voltages across the equivalent resistor and the buffer get smaller. Then the shaded area in FIG. 2 is approximately equal to the lost energy. Thereby, how to reduced the lost energy and achieve the purpose of saving the power consumption of the driving circuit have become the aims for current manufacturers.
Accordingly, the present invention provides a driving circuit for display panel, which provides a increasing driving power supply voltage to the data driving circuit of the driving unit during the charging process of the display panel for reducing excessive power consumption.